1. Field of the Invention
The present invention relates to an adaptive antenna apparatus including a plurality of sets of partial array antennas having different directivities, and in particular, to an adaptive antenna apparatus for use in a communication apparatus, typically including a mobile phone, and to a radio communication apparatus using such an adaptive antenna apparatus.
2. Description of the Related Art
Portable radio communication apparatuses such as mobile phones have rapidly miniaturized and become thinner. Further, the mobile radio communication apparatuses have developed into data terminal equipment that are not only used as conventional telephone sets, but for example, send and receive emails, and are used for browsing web pages of the WWW (World Wide Web). Since amounts of information to be handled increase from those of conventional audio and text information to those of pictures and movies, it is necessary to further improve the communication quality. Under such circumstances, it has been suggested to apply to the mobile terminal apparatus, an adaptive antenna apparatus which has so far been used mainly to enhance the performance of base station antennas.
For example, an antenna apparatus described in Japanese patent laid-open publication No. 11-284424 includes: a conductive housing; three antenna elements mounted at different locations of the conductive housing; a transmitting and receiving circuit mounted on the conductive housing and performing transmission and reception; and an amplitude and phase adjusting circuit connected to the antenna elements and the transmitting and receiving circuit and adjusting an amplitude and phase of each antenna element signal to reduce a radiation power in a direction of a user. This antenna apparatus is intended to solve problems including the waste of power which is converted into heat in a human head upon transmission without contributing to communication, the deterioration of reception characteristics due to mutual interference between delayed waves, etc. Accordingly, upon transmission, the antenna apparatus reduces the power to be radiated in the direction of the human head and thus can efficiently radiate signals transmitted to the antenna elements into space, and upon reception, the antenna apparatus has no directivity in the side of the mobile terminal toward the human body and thus can increase antenna directivity in directions other than that of the human body; and therefore, the antenna apparatus has an improved operational effect, i.e., an improvement of efficiency.
In addition, Japanese patent laid-open publication No. 10-242739, for example, proposes a configuration of an antenna apparatus in which in order to eliminate delayed waves which become interference waves, directional nulls are steered in the directions of delayed waves. This antenna apparatus has the following configuration of a mobile communication base station, to prevent the interferences of delayed waves, and to reduce the number of antenna elements for implementing pencil beams by using an array configuration. The antenna apparatus is configured as a base station antenna apparatus for mobile communication covering a strip-shaped area. In the antenna apparatus, a plurality of antenna elements, the number of which is between two and five, are linearly arranged so as to be orthogonal to a longitudinal direction of the strip-shaped area, and each distance between the antenna elements is set to a value between one wavelength and three wavelengths. In addition, an amplitude and phase adjuster, which changes the amplitude and phase of an input signal inputted from each antenna element through a frequency converter, is provided to each antenna input. Furthermore, an amplitude and phase calculating unit calculates the amplitude and phase of each antenna input signal so as to minimize an error between a signal which is known in advance by a receiving side and a combined signal of signals received by the respective antenna elements, and adjusts each amplitude and phase adjuster such that each amplitude and phase adjuster outputs a signal of each antenna element with the amplitude and phase calculated by the amplitude and phase calculating unit.
As a diversity of antennas having a plurality of antenna elements, there are antenna apparatuses such as those disclosed in Japanese patent laid-open publications Nos. 7-74687, 6-132940, 9-214409 and 6-502981.
According to such prior art antenna apparatuses, in general, since a plurality of antenna elements are arranged parallel to one another on a straight line, there is a problem that it is difficult to control the beams and nulls in the direction of the straight line passing through the antenna elements. This problem is particularly remarkable when the number of antenna elements is two.
FIG. 48 is a plan view showing a prior art array antenna apparatus, including two half-wavelength dipole antennas 31 and 32 arranged parallel to each other. FIGS. 49 to 52 are diagrams showing simulation results for the array antenna apparatus of FIG. 48. The array antenna apparatus of FIG. 48 includes the dipole antenna elements 31 and 32 each having an element length of λ/2 when the wavelength of a radio signal to be transmitted and received is λ, and the dipole antenna elements 31 and 32 are provided so as to be parallel to each other and separated by a distance of λ/2. The dipole antenna element 31 has, at its middle, a feeding point Q01, and includes element portions 31a and 31b each having an element length of λ/4, such that the feeding point Q01 is positioned between the element portions 31a and 31b. The dipole antenna element 32 also has, at its middle, a feeding point Q02, and includes element portions 32a and 32b each having an element length of λ/4, such that the feeding point Q02 is positioned between the element portions 32a and 32b. The following description is made using a coordinate system having x, y and z axes, as shown in FIG. 48. Here, a direction from back to front of the drawing is defined as a positive direction on the x-axis.
FIGS. 49 to 52 are diagrams each showing an example of a radiation pattern in a horizontal-plane (x-y plane) of the array antenna apparatus of FIG. 48 which is adaptively controlled when a desired wave with a certain azimuth angle and an interference wave with a certain azimuth angle are incoming to the array antenna apparatus. As incoming waves, one desired wave and one interference wave arrives with an interval of 40 degrees between these waves. Each of FIGS. 49 to 52 shows the case in which an average angle of arrival (i.e., a center angle between the desired wave and the interference wave) is 0, 45, 90 or 135 degrees. Specifically, FIG. 49 shows the case in which the desired wave with the azimuth angle of 20 degrees and the interference wave with the azimuth angle of −20 degrees are incoming to the array antenna apparatus of FIG. 48, FIG. 50 shows the case in which the desired wave with the azimuth angle of 65 degrees and the interference wave with the azimuth angle of 25 degrees are incoming to the array antenna apparatus of FIG. 48, FIG. 51 shows the case in which the desired wave with the azimuth angle of 110 degrees and the interference wave with the azimuth angle of 70 degrees are incoming to the array antenna apparatus of FIG. 48, and FIG. 52 shows the case in which the desired wave with the azimuth angle of 155 degrees and the interference wave with the azimuth angle of 115 degrees are incoming to the array antenna apparatus of FIG. 48. Each radiation pattern shows a vertically polarized component. The interference wave signal is uncorrelated with the desired wave signal, an initial value of a signal to noise ratio (SNR) is 20 dB, and an initial value of a signal to interference ratio (SIR) is 0 dB, i.e., a desired wave and an interference wave have the same signal level. Both the desired wave signal and the interference wave signal are QPSK signals.
The results of signal to interference plus noise ratios (SINR) after adaptive control are shown below.
TABLE 1Average Angle of ArrivalSINRBER(a)0 degree16.9 dB1.2 × 10−12(b)45 degrees16.9 dB1.5 × 10−12(c)90 degrees−0.3 dB1.6 × 10−1(d)135 degrees 16.9 dB1.2 × 10−12
It can be seen that when the average angles of arrival are 0, 45 and 135 degrees, the SINR is sufficiently improved by performing the adaptive control for steering a null in the direction of the interference wave, however, when an average angle of arrival is 90 degrees, a desired wave signal and an interference wave signal have almost the same signal level and thus the SINR is not improved. This results from the fact that in a linear array, the control of beams and nulls in an array direction is limited. Thus, in the case of the array antenna apparatus of FIG. 48, it can be seen that since a plurality of antenna elements are arranged so as to be aligned on the y axis, the beam and the null cannot be controlled on the incoming wave and the interference wave from the direction of y-axis (i.e., the direction of 90 degrees), as shown in FIG. 51.
As described above, a plurality of antenna elements of the prior art antenna apparatuses are generally arranged parallel to one another on a straight line, and thus there is a problem that it is difficult to control beams and nulls on the straight line passing through the antenna elements.